Rectilinear pulverizer



Oct. 5, 1954 J. B. CHATELAIN 2,690,880

' RECTILINEAR FULVERIZER Filed April 10. 1951 5 Sheets-Sheet 1 1s\ T fiT H INVENTOR.

JOHN B. CHATELAIN ATTOR NEY Get. 5, 1954 J. B. CHATELAIN RECTILINEARPULVERIZER Fild April 10, 1951 5 Sheets-Sheet 2 S R E L F H W W Imwf mNmOZEwuUxm .rzmummn.

FEED RATE IN LBS./HR./C.F.M. FREE AIR INVENTOR.

JOHN B CHATELAI N AT ORNEY Oct 5, 1954 J. B. CHATELAIN 2,690,880

RECTILINEAR PULVERIZER Filed April 10, 1951 5 Sheets-Sheet 3 INVENTOR.JOHN B. CHATELAIN ATTORNEY Oct. 5, 1954 J. a. CHATELAIN 2,690,380

RECTILINEAR PULVERIZER Filed April 10, 1951 5 Sheets-Sheet 4 f/ g. 6.INVENTOR.

JOHN B. CHATELAIN ATTORNEY at. 5, H54 4. B. CHATELAIN 2,690,880

RECTILINEAR PULVERIZER Filed April 10, 1951 5 Sheets-Sheet 5 H4 IOlWITHOUT FILLERS WITH FIL RS AVERAGE PARTICLE SIZE- MICRONS FEED RATE INLBSv/HR./C.F.M. FREE AIR INVENTOR.

JOHN B. CHATELAIN AT ToRNEY Patented Oct. 5, 1954 UNITED STATEh .EJATE@FFEQE RE CTILINEAR PULVEBIZER Ware Application April 10, 1951, SerialNo. 220,193

(El. mil-39) 5 Claims.

This invention relates to pulverizers and more particularly to thedesign of the grinding chamber for fluid jet operated pulverizing mills.

Fluid jet operated pulverizing mills of various shapes and designs havebeen known and used for many years. The present invention is directed tothe improvement of the efiiciency of this type of pulverizing mill. Thebasic criteria for determining the efficiency of these mills is theparticle size produced, the uniformity of the particle size, thepressure and volume of air required for operation and the rate thematerial can be passed through the mill. It is not sufficient merely toimprove the grinding character istics of the mill, in addition, theclassification must be improved, if a suitable product is to beobtained.

In existing designs of pulverizers, difiiculty has been experienced dueto the grinding chamber accumulating material between the grinding jets,

in its peripheral portions. This material accumulates until it extendsinto the main circulating stream of grinding fluid. When this occurs,the accumulated material is rapidly entrained into the circulatingstream of grinding fluid, much of it entering the classifying vortex andpassing to the collector without proper reduction in size. This resultsin an unsatisfactory product, due to the presence of a high percentageof oversize particles. This accumulation and periodic ejection, of theaccumulated material, occurs in the standard, fluid jet, pulverizingmill as a rhythmic cycle.

It is frequently more desirable to produce a product of uniform sizethan to grind the material as fine as possible. Many materials processedin this type of mill should not be reduced to the smallest particle sizepossible, but rather they should be reduced to particles of intermediatesize. In the case of many of these materials, however, it is criticalthat the particle size be uniform. An example of such a product ispenicillin, wherein the maintaining of an effective level in the bloodfor therapeutic purposes is largely dependent upon obtaining a producthaving a uniform particle size falling within a relatively narrow range.My invention is directed to obtaining a product having a high percentageof particles of uniform size while increasing the capacity of the mill.

To obtain this objective, it has heretofore been conventional practiceto increase the number of jets of grinding fiuid entering the grindingchamber. This, however, decreases the efficiency of the grinding action.Although the particle size Z of the final product is more uniform, therate of feed of the material through the pulverizer must be reduced toprevent the final product from being too large.

My invention overcomes this difficulty by reshaping the grinding chamberso that little or no area remains for the accumulation of material. Thismay be done by placing segment or filler blocks between the jets in theconventional circular grinding chamber or by initially so designing thechamber that its walls are noncircular and eliminate the areas ofaccumulation.

It is, therefore, a primary object of my invention to redesign theinternal shape of the grinding chamber of fluid jet, pulverizing millswhereby the material accumulating, peripheral pockets are eliminated.

It is a further object of my invention to reduce load fluctuations inthe grinding chamber.

It is an additional object of my invention to increase the capacity ofthese mills and at the same time to increase their grinding efiiciency.

It is a further, additional object of my invention to provide apulverizing mill capable of producing a product of more uniform size.

These and other objects and advantages of my invention will beimmediately seen by those acquainted with the design and operation offluid jet, pulverizing mills upon reading the following specificationand the accompanying drawings.

In the drawings:

Figure 1 is a central, sectional, elevation View of a mill equipped withmy segments.

Figure 2 is a sectional view taken along the plane 11-11 of Figure 1,not showing the means for anchoring the segments to the mill.

Figure 3 is a fragmentary, enlarged, sectional View of the nozzleinstallation in the mill shown in Figures 1 and 2.

Figure 4 is a central, sectional, elevation view of a mill equipped withfiller segments to provide a substantially square grinding chamber, andtaken along the plane IVIV of Figure 5.

Figure 5 is a sectional View taken along the plane V-V of Figure 4.

Figure 6 is a sectional, elevation view of a mill having a squaregrinding chamber and no fillers, taken along the plane VI--VI of Figure7.

Figure 7 is a sectional view taken along the plane VII--VII of Figure 6.

Figure 8 is a central, sectional view of a mill having a triangulargrinding chamber.

Figure 9 is an enlarged, sectional, elevation View taken along the planeIXIX of Figure 8.

Figure 10 is a central, sectional View of a modified mill parallel toone of the end plates of the mill.

Figure 11 is a performance graph.

Figure 12 is a performance graph.

In executing the objects and purposes of my invention, I have provided afluid jet pulverizing mill having a noncircular grinding chamber. Theflat segments of the grinding chamber walls are spaced between the jetsof grinding fluid entering the grinding chamber. Depending upon the sizeof the grinding chamber and the number of jets used, the shape of thegrinding chamber may be a polygon, square or triangle.

In the following description, the terms inwardly and outwardly arefrequently used and shall be taken to mean inward1y as toward thegeometric center of the mill and outwardly away therefrom.

Although the views of the mills are shown and described as though thegeneral plane of the mill were horizontal, this is merely for simplicityand convenience and is not to be considered as a limitation. Generally,the mills may be operated in either a horizontal or vertical planewithout modification of their structure.

Referring now specifically to the drawings, the numeral 1 indicates afluid jet mill having a central grinding chamber 2 enclosed on each ofits ends by plates 3 and 4 and about its circumferential periphery bythe circular bafiie 5 (Figures 1 and 2). The end plates 3 and 3 eachproject a substantial distance beyond the circular baflle 5, and, abouttheir periphery, are joined by the circular wall 6. An annular chamher Iis defined between the end plates 3 and circular baiile 5 and circularwall 6. A grinding fluid inlet port 8 provides means for admitting thegrinding fluid to the annular chamber 1 (Figure 2). The material to bepulverized is admitted through the conduit 9 which communicates with thegrinding chamber 2 through the plate 3. This conduit is positioned tofeed the material into the vortex of grinding fluid moving within thegrinding chamber, which vortex of grinding fluid will be described morefully hereinafter. It will be understood that the conduit 9 is merely aschematic showing of the material feeding means. Several difierent typesof material feeding means may be used according to the requirements ofthe pulverizer. Since the material feeding means forms no part of thisinvention a more detailed description is not believed necessary.

A plurality of replaceable nozzles [5 are mounted through openings [6,in the circular bafile 5, substantially midway between the plates 3 and4 (Figures 1, 2 and 3). The openings !6 in the circular baiile 5 and thenozzles 15, are each tapered, with the end of smaller diameterpositioned inwardly of the mill, whereby the nozzles l5 will be held inposition by engagement of the nozzle surface with the walls of theopening it. Each of the nozzles i5 is provided with a central passagewayI! for grinding fluid. The size of the passageway l1 will depend uponthe size of the grinding chamber, the number of nozzles employed, thepressure of the grinding fluid and the velocity desired. The face of theinward end of each of the nozzles is perpendicular to the passageway l1.

Coaxial with each of the nozzles I5, an access opening I8 is providedthrough the circular wall 6. The access openings i8 are of largerdiameter than the nozzles 15, whereby the nozzle may be passed throughit during servicing or replacement. The internal walls of each of theaccess openings it are threaded for seating the plugs IS.

The number of nozzles provided depends in part upon the size of the milland in part upon the type of grinding desired and the material to betreated. The shape of the grinding chamber, normally, is dependent uponthe number of nozzles. In the large size mill, l, eight, equally spacednozzles l5 are provided. The axis of each of the nozzles I5 is inclinedto the circular baifie 5 and tangent to the circle 28 of circulatinggrinding fluid and entrained material within the grinding chamber 2. Thediameter of the circle 20 is that which provides the most efiicientvortex for grinding and classifying. Within the circle 26 and concentrictherewith, is the ofitake conduit 2| for leading the fines and the spentgrinding fluid from the grinding chamber to a suitable collector ofconventional design. At the collector, the fines and the grinding fluidare separated. The offtake conduit 2| is of substantially smallerdiameter than the circle 20 and projects into the grinding chamber 2 adistance more than onehalf the spacing between the plates 3 and 4.

The circular grinding chamber is rendered 0ctagonal by the installationof the constricting segments or fillers 25. Each of the fillers 25 isarcuate along one side to snugly engage the circular baflle 5 andstraight along the side facing into the grinding chamber 2. The fillers25 are each provided with a hole to permit a nozzle Hi to projectthrough it to the flllers inward surface. The flllers are held in placeby means of the screws 28 (Figure 3). Each of the fillers 25 seatstightly against the end plates 3 and 4, whereby no material can collectbetween these parts or work behind the fillers.

The pulverizing mill 3%, shown in Figures 4 and 5, is quite similar tothe pulverizing mill 1, except that it has a substantially squaregrinding chamber 3!. Like the pulverizing mill I, it has a grindingchamber 3| surrounded by an annular chamber 32. The annular chamber 32and grinding chamber 31 are separated by a circular baiile 33. Theannular chamber is enclosed by the outer wall 34 and the end plates 35and 36. A suitable inlet port 38 is provided through the outer wall 34for the grinding fluid.

Four, equally spaced, nozzles 31 connect the annular chamber 32 with thegrinding chamber 3| tln'ough the holes 44. Each of the nozzles istapered whereby they may be removed for cleaning or replacement. Accessholes 39 are provided through the outer wall 3 to permit installationand removal of the nozzles. Each of the access holes is closed by athreaded plug 48. The axis of each of the nozzles 31 is at a right angleto the axis of each of its adjacent nozzles, and all are tangent to acircle 45 within the grinding chamber.

The nozzles 31 each have a concentric passageway 4] for the admission ofgrinding fluid to the grinding chamber. The discharge oriflce 42, of thenozzles 31, is substantially smaller than the passageway 4! to increasethe velocity of the jet of grinding fluid entering the grinding chamber.One corner 43 of each of the nozzles 31 is chamfered so that no portionof the nozzle will project into the circulating stream within thegrinding chamber. The major portion of the inward face of each of thenozzles 31, however, is perpendicular to the passageway M.

The grinding chamber 3| is equipped with four constricting segments orfillers 50, each fitting snugly against the circular baflie 33 and theend plates and 38. Each of the fillers 58 has one end at one of theopenings 83 for a nozzle 31 and its flat side parallel to the axis ofthe passageway 48 of the same nozzle. The fillers 44 are secured to thecircular baflle 33 by screws 41.

Material to be pulverized is fed into the grinding chamber 3i by meansof the screw feed 48. The screw feed is located approximately on thecircle representing the primary path of circulating grinding fluid andmaterial. It will be recognized that any suitable feeding mechanism maybe substituted for the screw type feed. The fine, pulverized material isremoved from the grinding chamber 3I by the oiftake conduit 48, locatedat the center of the grinding chamber and extending through the endplate 36. The offtake conduit connects with any suitable, conventionalseparator. The diameter of the ohtake conduit 48 is substantially lessthan that of the circle 85. The oiftake conduit projects into thegrinding chamber slightly more than one-half the distance between theend plates 35 and 38.

The pulverizing mill 88 (Figures 6 and 7) is quite similar to the mill38 except that the fillers 58 have been eliminated and the grindingchamber 81 is a true square instead of being substantially square. Thefillers are replaced by a jacket 88 having an internal square openingdefining the grinding chamber 8I. end plates 82 and 83, joined abouttheir periphery by an outer wall 88. A grinding fluid inlet means 85 isprovided through the outer Wall 84. The jacket 88 has a circular outersurface. An annular grinding fluid chamber 88 is defined between thejacket 86 and the outer wall 84. A replaceable nozzle 89 is mounted ateach corner of the grinding chamber BI. Each of the nozzles is tangentto the circle 98 representing the circular path traced by the grindingfluid in the grinding chamber. An outlet conduit 9| connected to asuitable, conventional collector provides means for withdrawing thefines from the grinding chamber.

Access openings 92 are provided through the outer wall 88 for each ofthe nozzles 89 to permit replacement. Each of the access openings 82 isclosed by means of a plug 93. Any suitable means may be provided forfeeding material into the grinding chamber 8| such as the screw feed 94.

The pulverizing mill I88 is designed to have a substantially triangulargrinding chamber. The mill I88 includes a pair of slightly concave endplates IM and I82, separated by a pair of concentric rings, the circularbafiie I83 and the outer wall I84. A grinding chamber I85 is enclosedwithin the circular bafile I83 between the end plates MI and I82. Anannular chamber I86 is defined between the end plates I8I and I82, thecircular bafile I83 and the outer wall I84. A grinding fluid inlet portI I8 is provided through the outer wall I84.

Three small orifices I87 pass at an angle through the circular bafileI83 for admitting grinding fluid from the annular chamber I88 to thegrinding chamber I05. The centerline of each of the orifices I81 isinclined at the same angle and in the same direction whereby they areeach tangent to a circle I88 of substantially lesser diameter than thatof the circular baflle I83. Within the circle I88, and of substantiallylesser diameter, is the offtake conduit I89 which is connected to asuitable, conventional collector. It will be understood that theorifices I81 The mill 88 has could be enlarged and removable nozzlesused to direct the grinding fluid as is shown in mills I and 38.

The grinding chamber is equipped with three constricting segments orfillers I I4, spaced about the periphery of the grinding chamber andattached to the circular baiile I83 by means of screws II5. Each of thefillers H4 is cross-sectionally, wedge shaped to seat snugly against theconcave surfaces of the end plates I8I and I82. The fiat surface of eachof the fillers I I4, is parallel to the axis of one of the orifices I81but spaced a short distance radially outwardly from the circle I88. Theend plates I8I and I82 may be made straight so that the inward faces ofthe plates are parallel. When this construction is employed, the fillersII4 are made with parallel end faces eliminating the wedge shapedconstruction.

In the construction of each of these mills, it will be understood thatthe nozzles, although preferably replaceable, are not necessarily so.They may be made permanent. When replaceable nozzles are used, means foranchoring the nozzles to the circular bafile other than a frictional fitmay be used. One substitute method of attachment could be by means ofthreading.

In the construction of each of the above described mills the fillersegments may be designed to have a slightly curved inward face. Thisdesign, however, is not considered preferable. Any such curvature shouldbe slight, otherwise much of the benefit of utilizing the segments willbe eliminated. Another feature of construction appearing throughout theabove description is the use of a collector designed as a separateelement distinct from the pulverizing mill. It is also possible to mountthe collector directly on the pulverizing mill as an attachment to it.Such a construction is not illustrated because whether the collector isan independent element or an attachment to the mill is immaterial to theinvention disclosed herein.

OPERATION The operation of each of the pulverizing mills I, 38, 88* andI88 is similar. Therefore, a single description will sufiice for all. Ingeneral, the mills each operate on the same principles and in the samegeneral manner as conventional, fluid jet pulverizers. A pressurizedgrinding fluid, normally air or steam, is admitted to the annularchamber. Although air and steam are the most commonly used grindingfluids, it will be recognized that any of the grinding fluid may beemployed if the operation requires it. The grinding fluid is theninjected into the grinding chamber through the nozzles, in the case ofmills i, 38 and 88 or through the orifices in the case of the mill I88.In each of the mills the grinding fluid enters the grinding chamber at ahigh velocity. Since each of the entering streams or jets of grindingfluid is inclined in the same direction, a high velocity, circular pathis established in the grinding chamber. All of the jets may be tangentto a single circle or some of the jets may be tangent to one circle andthe other jets tangent to another circle or circles. The circulatingstream entrains the particles of material fed into the grinding chamber.The particles are reduced in size by the impact of the grinding fluidand by collision between particles. The smaller particles, commonlyknown as fines, enter into the vortex formed between the primary path ofcirculating grinding fluid and the oiftake conduit and are carried oifto a collector. This vortex serves as the classifier for the particles.

The larger particles, commonly known as heavies, are by centrifugalforce, caused to migrate toward the periphery of the grinding chamber.In mills of conventional design, these heavies tend to accumulate inmasses between the primary path or paths of circulating grinding fluidand the walls of the grinding chamber in the spaces between the jets.These masses of oversize particles grow in size until they extend intothe path of circulating grinding fluid. These masses of heavy particlesthen break free and pass into the circulating stream. Since theeflicient operation of one of these mills requires a constant balancebetween the quantity and velocity of grinding fluid and the rate atwhich the material is processed through the mill, this overloading ofthe circulating stream seriously disrupts the balance between thequantity of entrained material and the volume of grinding fluid. Thisoverloading temporarily destroys classifying vortex, permitting largequantities of the heavies to escape into the off-take conduit withoutproper reduction in size. The result is a product of widely varyingparticle size.

By placing the fillers in the grinding chamber, all or a substantialportion of the area within which this material is able to accumulate iseliminated. Thus, the loading of the grinding chamber will remainsubstantially constant, and a final product of more uniform size will beproduced. All of the material passing through the mill is reduced to asubstantially uniform size. The periodic flooding of heavy particlesinto the classifying vertex is eliminated. This uniformity of thegrinding chamber load factor cannot be accomplished without the use ofthe fillers and, without this uniformity of load factor, the uniformityof product cannot be obtained. The fillers are situated radiallyoutwardly of the primary path of the vortex of grinding fluid. When thestream of grinding fluid is caused to im-- pinge directly upon thefillers, excessive wear of the fillers and contamination of the materialoccurs.

The use of the fillers or their functional equivalent, the noncirculargrinding chamber permits the number of jets to be reduced. The smallerthe number of jets employed, the greater the grinding efliciency of themill. However, heretofore the efficiency in grinding resulting from theelimination of some of the jets was more than offset by the reduction inclassification efliciency. As the number of jets was reduced the totalarea for accumulation of material about the periphery of the grindingchamber increased and thus, the problem of periodic overloading of thegrinding chamber became more acute. With the use of the fillers,however, the number of jets may be decreased without increasing the areaof accumulation. Thus, while the grinding efiiciency of the mill isincreased, the classification of the mill may also be increased. Thefillers permit the load in the grinding chamber to be reduced to aminimum, thus, utilizing a maximum portion of the energy of the grindingfluid for accelerating the particles. This causes a substantial increasein the overall eficiency of the mill.

Excessive wear of the grinding chamber walls has always been a seriousproblem in fluid jet pulverizers, particularly when there is impingementof the fluid jet against the grinding chamber walls. Even the use ofspecial, hard, wear resistant alloys does not eliminate this problem,merely alleviating it. Where the wearing surfaces of the grindingchamber walls are an integral part of the pulverizers construction, thereplacement cost is high. With the use of the fillers, this difficultyis overcome because only the fillers need be made of the special alloyand these fillers can be easily replaced.

Example I Two separate test runs were made using cold air to grindcalcite. Both runs were made with air at the same pressure and admittedto the grinding chamber at the same rate. The first test run was made ina conventional mill having an 8 inch diameter circular grinding chamberequipped with four No. 29 drilled nozzles in the peripheral wall tangentto a 5 /2 inch diameter circle. The nozzles were drilled openings, noreplaceable nozzle structure being used.

The second test run was made with a mill having a 6 inch square grindingchamber equipped with four replaceable nozzles tangent to a 5 /2 inchdiameter circle. Each of the replaceable nozzles had a No. 29 drilledhole. The inward face of each of the nozzles was perpendicular to theaxis of the hole through the nozzle.

The results of these two test runs are tabulated below:

Percentage of Product in Exper minut First Test Run Second Test Run Itis seen from this comparison that a very substantial improvement in theuniformity of the product was obtained. The comparative improvement inuniformity increased as the feed rate was increased. Some of theimprovement may have been due to the use of the square end nozzles inthe mill having the square grinding chamber. However, this factor willaccount only for a minor portion of the improved results.

Example II Two test runs were made grinding 99 sulphur and 1% tritonX-l66. In both runs air was used as the grinding fluid at a flow rate ofapproximately 103 cubic feet per minute, free air. Both runs were madein a vertical mill having an 8 inch diameter grinding chamber. The firstrun was made without fillers. The second run was made with fillers asshown in Figures 4 and 5. Both mills were equipped with four replaceablenozzles tangent to a 6 inch diameter circle. The improvement in theproduct, from the standpoint of uniformity of particle size, isgraphically presented in Figure 11. The improvement in the product fromthe standpoint of reduction of the average particle size is graphicallypresented in Figure 12.

Example III Two test runs were made grinding procaine penicillin, withthe objective of producing a product having a particle size between 20and 50 microns and a maximum particle size of 100 microns- The first runwas made with a. two inch Product Size Distribution in Microns MaximumLesszghan 20-50 50-120 Percent Percent Perccm First run 120 50 45 Secondrun 5O 30 70 0 From this test it is seen that not only may the grindingrate be accelerated but a product of more uniform particle size can beobtained, reducing the quantity of both undersize and oversizeparticles.

The improvement in the product due to the addition of the fillers ismuch more than an incidental improvement. The improvement not onlyproduces a better product at the slower feed rates but the degree ofimprovement between the two products increases as the feed rate isincreased.

MODIFICATIONS It will be recognized that the fillers described in themills i, 30 and I00 may either be used as standard equipment in newmills of circular de sign or may be used for converting existingcircular mills. It is also possible to design new mills equipped withnoncircular grinding chambers without employing the fillers. Such a millis shown in Figures 6 and '7. It is also possible to construct a millhaving a noncircular grinding chamber using plate material for thejacket defining the grinding chamber. Such a mill I20 (Figure 10) willhave the conventional end plates and a circular outer wall 123 providedwith a grinding fluid inlet I24. The wall I25, however, separating thegrinding chamber I26 from the grinding fluid chamber I2? is formed toprovide the desired shape of the grinding chamber. This wall i25 can beshaped to provide any one of the desired, noncircular, geometric shapes.In this way, the fillers can be dispensed with and the same improvementin operation obtained.

These and other modifications of my invention may be made withoutdeparting from the principle of my invention. Each of the modificationsis to be considered as included in the hereinafter appended claimsunless these claims by their language expressly state otherwise.

I claim:

1. In a fluid jet pulverizer having a material inlet conduit and anofftake conduit, the combination including: a rectilinear grindingchamber; a plurality of jets for admitting gas under pressure to saidgrinding chamber, each of said jets being arranged tangential to atheoretical circle of greater diameter than said offtake conduit andconcentric therewith, to form a classifying vortex within said grindingchamber.

In a fluid jet pulverizer having a material inlet conduit and an oiftakeconduit the combination including: a wall defining a rectilineargrinding chamber and. a plurality of jets therethrough for admitting gasunder pressure to said grinding 10 chamber, each of said jets beingtangential to a theoretical circle of greater diameter than said offtakeconduit and concentric therewith to form a classifying vortex withinsaid grinding cham- ,ber; and each of the straight portions of saidwalls of said grinding chamber being substantially parallel to the axisof one of said jets.

3. In a fluid jet pulverizer having a material in- ;let conduit and anoiftake conduit the combination including: a wall defining a rectilinearrind- ,ing chamber; a member for substantially closing .each of the endsof said grinding chamber; a plurality of jets through said walls foradmitting a gas under pressure to said grinding chamber, .forming aclassifying vortex within said grinding chamber, the number of jetsbeing equal to the number of straight portions of the said walls of saidgrinding chamber and arranged tangential to a theoretical circle ofgreater diameter than said ofitake conduit; each of the said straightportions of said grinding chamber being substantially parallel to theaxis of one of the said jets.

4. In a fluid jet pulverizer having a circular Wall defining a grindingchamber therein and members substantially closing the ends of saidgrinding chamber except for inlet and offtake conduits, a plurality ofjets through said circular wall for admitting grinding fluid to saidgrinding ,chamber, each of said jets tangent to a circle of greaterdiameter than said ofitake conduit within said grindin chamber, theimprovement in said pulverizer including: a plurality of segmentalfillers mounted about the periphery of ,said grinding chamber, thearcuate face of each of said fillers being mounted against said circularWall, the chord face of each of said fillers being substantiallyparallel to one of said jets and radially outwardly of said circle; thenumber of .said fillers and of said jets being equal; and, said jetseach extending through one of said filler plates and into said grindingchamber arranged to form a classifying vortex within said grindingchamber.

5. In a pneumatic pulverizer having a material inlet conduit and anoiftake conduit the combination including a wall defining a rectilineargrinding chamber and a plurality of openings through said wall foradmitting gas under pressure to said grinding chamber; a removablenozzle having a central passageway therethrough mounted in 1 each ofsaid openings; the face of said nozzle directed toward said grindinchamber being per- ,pendicular to said central passageway; the centralpassageway of each of said jet being tangential to a circle of greaterdiameter than said oiftake conduit and arranged to form a classifyingvortex within said grinding chamber.

